Signaling of measurement signals based on a tree structure

ABSTRACT

One or more nodes transmit CSI-RS symbols in a set of N CSI-RS elements, each CSI-RS element in the set corresponding to at least one resource element in a time-frequency grid of resource elements. The nodes select, from the N CSI-RS elements, a first set of CSI-RS elements to be measured by a first wireless device, the first set comprising one or several of the N CSI-RS elements. The nodes also transmit, to the first wireless device, a message comprising a first K-bit indicator identifying the first set of CSI-RS elements, wherein K&lt;N. The nodes then receive a measurement report. The first K-bit indicator is one of a predetermined set of K-bit indicators, where each member of the predetermined set of K-bit indicators uniquely corresponds to a CSI-RS element or group of CSI-RS elements from among the N CSI-RS, according to a predetermined mapping.

TECHNICAL FIELD

The present disclosure is generally related to wireless communicationsnetworks and is more particularly related to techniques for controllingthe measurement of channel-state information reference signals (CSI-RS)in such networks.

BACKGROUND

In the Long-Term Evolution (LTE) wireless communications systemstandardized by members of the 3^(rd)-Generation Partnership Project(3GPP) and widely deployed today, a reference symbol sequence referredto as a Channel-State Information Reference Signal (CSI-RS) istransmitted by the base stations (referred to as eNodeB's, or eNBs, in3GPP terminology). These CSI-RS are measured by receiving wirelessdevices (“user equipment,” or “UEs,” in 3GPP terminology), with theresulting measurements being used to estimate the channel from the basestation to the wireless device. Importantly, these measurements reflectnot only the propagation conditions from the antennas of the basestation to the wireless device, but also reflect the antenna gains,polarization, and any multi-antenna aspects of the transmission.Accordingly, by mapping different antennas or different combinations ofantennas to different CSI-RS elements and configuring a UE to measureand report on each of these elements, the network can determine whichantennas or combinations of antennas provide the most effective channelto the UE.

A CSI-RS targeted to a particular UE or group of UEs may be referred toas non-zero-power CSI-RS (NZP CSI-RS). A UE may also be configured with(i.e., informed of) so-called zero power CSI-RS (ZP CSI-RS). The ZPCSI-RS is mainly used for interference measurement resource indication.A ZP CSI-RS for one UE may correspond to a (NZP) CSI-RS for one or moreother UEs within same the cell or within a neighbor cell. A UE for whicha ZP CSI-RS resource has been configured should assume that physicaldownlink shared channel (PDSCH) mapping avoids the resource elementscorresponding to the ZP CSI-RS, as well as any resource elements withNZP CSI-RS.

The NZP CSI-RS is not used for demodulation of the data signal, and thusdoes not require the same density (i.e., the overhead of the NZP CSI-RSis substantially less) as the demodulation RS (DMRS). Compared to DMRS,NZP CSI-RS provides a much more flexible means to configure CSI feedbackmeasurements. For instance, the network may configure, in a UE-specificmanner, which particular NZP CSI-RS the UE should measure, of severalavailable NZP CSI-RS resources to the UE.

By measuring on a NZP CSI-RS, a UE can estimate the effective channelthe NZP CSI-RS has traversed, including the radio propagation channeland antenna gains. In mathematical terms, this means that if a known NZPCSI-RS signal x is transmitted, a UE can estimate the coupling betweenthe transmitted signal and the received signal (i.e., the effectivechannel). Hence, if no virtualization is performed in the transmission,the received signal y can be expressed as:y=Hx+e,  (Eq. 1)and the UE can estimate the effective channel H.

In LTE, as of Release 11 of the 3GPP specifications, up to eight NZPCSI-RS ports can be configured for a UE, where a “port” corresponds to apredefined set of resource elements in the Orthogonal Frequency-DivisionMultiplexing (OFDM) time-frequency grid that makes up each subframe ofthe LTE downlink signal. At the network side, the eNB can map anytransmit antenna or combination of transmit antennas to a given port.Thus, by performing measurements on the specific resource elements thatcorrespond to each CSI-RS port that is configured for the UE, a UEconforming to Release 11 of the 3GPP specifications for LTE can thusestimate the channel from up to eight transmit antenna ports.

As seen in FIGS. 1A, 1B, and 1C, many different NZP CSI-RS patterns areavailable in LTE, where the mapping of the CSI-RS ports to the LTEdownlink subframe depends on whether two, four, or eight CSI-RS portsare in use. (Herein, the terms “CSI-RS port,” “CSI-RS antenna port,” and“antenna port” may be used interchangeably, to refer to the particularresource elements that are identified as a particular CSI-RS measurementresource and that are implicitly mapped to a transmit antenna orcombination of antennas at the eNB). More particularly, FIGS. 1A-1Cillustrates the time-frequency resource element grid for the LTEdownlink signal, over a resource block pair, for the cases of two, four,and eight CSI-RS ports.

From FIG. 1A, it can be seen that for the case of two CSI-RS antennaports, there are twenty different patterns within a subframe; a given UEmay be configured to measure any one or more of these, and may befurther configured with information indicating that one or more of theseare ZP CSI-RS resources, with respect to that particular UE. Thecorresponding number of patterns is ten and five, for configurationsinvolving four and 8 CSI-RS antenna ports, respectively. This is shownin FIGS. 1B and 1C. For LTE systems operating in a Time-DivisionDuplexing (TDD) configuration, some additional CSI-RS patterns areavailable.

3GPP has begun developing specifications for a new fifth-generation (5G)radio access technology, currently referred to as “New Radio,” or NR.Members of 3GPP have reached initial agreements on a few designprinciples for NR, including that it should utilize an “ultra-lean”design, in that the transmission of “always-on” signals should beminimized or eliminated. Further, it is a common understanding that NRwill consider frequency ranges up to 100 GHz. In comparison to thecurrent frequency bands allocated to LTE, some of the new bands willhave much more challenging propagation properties such as lowerdiffraction and higher outdoor/indoor penetration losses. Consequently,signals will have less ability to propagate around corners and penetratewalls. In addition, in high frequency bands, atmospheric/rainattenuation and higher body losses render the coverage of NR signalseven spottier. Fortunately, operation in higher frequencies makes itpossible to use smaller antenna elements, which enables the deploymentof antenna arrays with many antenna elements at the NR access nodes,which may be referred to herein as “gNBs.” Such antenna arraysfacilitate beamforming, where multiple antenna elements are used to formnarrow beams and thereby compensate for the challenging propagationproperties. For these reasons, it is widely accepted that NR will relyon beamforming to provide coverage, which means that NR is oftenreferred to as a beam-based system.

In NR, a similar approach to channel state estimation as employed in LTEis foreseen. However, in NR, the downlink signal is not expected toinclude cell-specific reference signals (CRS), which are distributedthroughout the LTE subframes. This means that the placement of CSI-RScan be more flexible than in LTE.

There have been discussions on placing the NZP CSI-RS in one or a fewOFDM symbols of the NR downlink subframe. FIG. 2, for example,illustrates the placing of CSI-RS in one OFDM symbol of a slot (sevensymbols one-half of a subframe). As seen in the figure, the first OFDMsymbol contains the control channel, which carries downlink controlinformation (DCI) for UEs, while the next OFDM symbol carriesdemodulation reference signals (DMRS) for use by the UEs in demodulatingthe control channel. The third symbol in the illustrated example carriesCSI-RS symbols.

A CSI-RS resource or CSI-RS element includes reference signals for oneor multiple antenna ports. The reference signal may be repeated over thewhole frequency bandwidth or in a predefined or configurable partialbandwidth. Note that the terms “CSI-RS resource” and “CSI-RS element”should not be confused with the term “resource element,” which is usedherein to refer to the smallest time-frequency resource in an OFDMtime-frequency grid.

One possibility for creating a CSI-RS resource is that a CSI-RS elementthat has two antenna ports is introduced. CSI-RS configurations with anarbitrary number of antenna ports can be obtained by aggregating CSI-RSelements. Note that an antenna port is equivalent to—or may beunderstood as an abstraction of—a reference signal. If the UE measures“an antenna port,” it measures the channel from the transmitter to thereceiver for that given antenna port. If spatial transmit diversity isused, for example, then typically two distinct antenna ports are used toprovide spatial diversity, meaning that the UE has to estimate twochannels to demodulate the message.

In FIG. 2, each CSI-RS could correspond to a distinct antenna port, inwhich case the figure shows a total of twelve CSI-RS antenna ports thatare frequency multiplexed. Given this example configuration for thedownlink signal, the UE can be configured to measure on one of theseCSI-RS ports or on all twelve CSI-RS ports, depending on the use case.The twelve CSI-RS resources, each with a single antenna port, can thusbe seen as a pool or a set of CSI-RS resources.

When beamformed CSI-RS is used, each beam typically has twopolarizations, if a dual-polarized antenna array is used. A beam iscreated by a certain multi-antenna precoder, such as a discrete Fouriertransform (DFT)-based precoder. Hence, different ones of such precoders,having DFT structures, generate transmitted beams pointing in differentazimuth directions. Sometimes a two-dimensional antenna array is usedwith phase-controllable antenna elements and a DFT precoder is used inboth a vertical and horizontal direction, so that a beam can be steeredin the desired elevation and azimuth direction. A CSI-RS element havinga size of two ports can be used per beam, in such systems, and in thiscase each group of two ports may correspond to a different beam. The UEcan then be configured to measure and report the channel quality foreach beam in a set of beams by using a CSI-RS resource of aggregated2-port CSI-RS elements.

If non-beamformed CSI-RS is used, then a larger number of ports, e.g.,32, is needed. The aggregation of CSI-RS elements with two ports each isuseful also in this case.

While details have not been established, 3GPP members have discussed theuse of a set (or a pool) of CSI-RS resources, together with dynamicsignaling from gNB to the UE regarding which resource the UE shall usefor performing measurements. If the pool is large, however, thesignaling overhead is undesirably large. For instance, if the poolconsists of 32 resources, then a bitmap of 32 bits is needed to signalany arbitrary configuration of the selected resources. This creates alarge signaling overhead. Another problem is that the need formeasurements is UE-specific, as well as time-dependent. Sometimes it issufficient to measure a single resource and sometimes a large set ofresources is needed. Accordingly, solutions are needed for providingsuch flexibility in the signaling, while reducing signaling overhead.

SUMMARY

Some embodiments of the presently disclosed techniques and apparatusaddress these problems by adopting a tree structure for CSI-RS elementaggregation, to allow for CSI-RS configurations of variable aggregationsize, where the tree structure is defined in such a way that a largeraggregation size overlaps with an aggregation of smaller aggregationsize. The tree structure is motivated by field measurements onbeamforming, which have demonstrated that not all beams are equallyutilized in practical deployments, which means that there is acorrelation among preferred beams.

According to various embodiments, then, the signaling from gNB to UEutilizes an index mapping to the tree structure. After performingmeasurements on the aggregated CSI-RS resources indicated by the index,the UE may perform a subset selection of the resources and then reportback to the gNB the result or results of the measurement. As will bedemonstrated in detail below, this signaling approach results in areduction of the signaling overhead in configuring resources used forCSI measurements, compared to the use of a bitmap that would permit thesignaling of any arbitrary configuration of CSI-RS resources.

According to some embodiments, a method for controlling the measurementof CSI-RS elements in a wireless communication network includes, in oneor more nodes of the wireless communication network, transmitting CSI-RSsymbols in each of N CSI-RS elements, each CSI-RS element in the setcorresponding to at least one resource element in a time-frequency gridof resource elements. The method also includes selecting, from the NCSI-RS elements, a first set of CSI-RS elements to be measured by afirst wireless device, the first set comprising one or several of the NCSI-RS elements and transmitting, to the first wireless device, amessage comprising a first K-bit indicator identifying the first set ofCSI-RS elements, wherein K<N. The method further includes receiving,from the first wireless device, in response to the message, ameasurement report corresponding to at least one of the first set ofCSI-RS elements. The first K-bit indicator is one of a predetermined setof K-bit indicators, where each member of the predetermined set of K-bitindicators uniquely corresponds to a CSI-RS element or group of CSI-RSelements from among the N CSI-RS, according to a predetermined mapping,such that each member of a first subset of the predetermined set ofK-bit indicators uniquely indicates a single one of the N CSI-RSelements and such that each member of a second subset of thepredetermined indicators uniquely indicates a predetermined group of twoor more of the N CSI-RS elements.

According to some embodiments, a method for measuring CSI-RS elements ina wireless communication network includes, in a wireless device,receiving, from the wireless communication network, a message comprisinga first K-bit indicator. The method also includes using the first K-bitindicator to identify a first set of CSI-RS from N CSI-RS elements,wherein each CSI-RS element corresponds to at least one resource elementin a time-frequency grid of resource elements and wherein K<N. Themethod further includes performing measurements on the identified firstset of CSI-RS elements and sending, to the wireless communicationsnetwork, a measurement report corresponding to at least one of the firstset of CSI-RS elements. The first K-bit indicator is one of apredetermined set of K-bit indicators, where each member of thepredetermined set of K-bit indicators uniquely corresponds to a CSI-RSelement or group of CSI-RS elements from among the N CSI-RS, accordingto a predetermined mapping, such that each member of a first subset ofthe predetermined set of K-bit indicators uniquely indicates a singleone of the N CSI-RS elements and such that each member of a secondsubset of the predetermined indicators uniquely indicates apredetermined group of two or more of the N CSI-RS elements.

According to some embodiments, one or more nodes of a wirelesscommunication network configured to control the measurement of CSI-RSelements in a wireless communication network includes transceivercircuitry and processing circuitry operatively associated with thetransceiver circuitry. The processing circuitry is configured totransmit CSI-RS symbols in each of one or more of N CSI-RS elements,each CSI-RS element in the set corresponding to at least one resourceelement in a time-frequency grid of resource elements. The processingcircuitry is also configured to select, from the N CSI-RS elements, afirst set of CSI-RS elements to be measured by a first wireless device,the first set comprising one or several of the N CSI-RS elements andtransmitting, to the first wireless device, a message comprising a firstK-bit indicator identifying the first set of CSI-RS elements, whereinK<N. The processing circuitry is configured to receive, from the firstwireless device, in response to the message, a measurement reportcorresponding to at least one of the first set of CSI-RS elements. Thefirst K-bit indicator is one of a predetermined set of K-bit indicators,where each member of the predetermined set of K-bit indicators uniquelycorresponds to a CSI-RS element or group of CSI-RS elements from amongthe N CSI-RS, according to a predetermined mapping, such that eachmember of a first subset of the predetermined set of K-bit indicatorsuniquely indicates a single one of the N CSI-RS elements and such thateach member of a second subset of the predetermined indicators uniquelyindicates a predetermined group of two or more of the N CSI-RS elements.

According to some embodiments, a wireless device configured to measureCSI-RS elements in a wireless communication network includes transceivercircuitry and processing circuitry operatively associated with thetransceiver circuitry. The processing circuitry is configured toreceive, from the wireless communication network, a message comprising afirst K-bit indicator. The processing circuitry is configured to use thefirst K-bit indicator to identify a first set of CSI-RS from N CSI-RSelements, where each CSI-RS element corresponds to at least one resourceelement in a time-frequency grid of resource elements and wherein K<N.The processing circuitry is also configured to perform measurements onthe identified first set of CSI-RS elements and sending, to the wirelesscommunications network, a measurement report corresponding to at leastone of the first set of CSI-RS elements. The first K-bit indicator isone of a predetermined set of K-bit indicators, where each member of thepredetermined set of K-bit indicators uniquely corresponds to a CSI-RSelement or group of CSI-RS elements from among the N CSI-RS, accordingto a predetermined mapping, such that each member of a first subset ofthe predetermined set of K-bit indicators uniquely indicates a singleone of the N CSI-RS elements and such that each member of a secondsubset of the predetermined indicators uniquely indicates apredetermined group of two or more of the N CSI-RS elements.

Further aspects of the present invention are directed to an apparatus,computer program products or computer readable storage mediumcorresponding to the methods summarized above and functionalimplementations of the above-summarized nodes and wireless device. Ofcourse, the present invention is not limited to the above features andadvantages. Those of ordinary skill in the art will recognize additionalfeatures and advantages upon reading the following detailed description,and upon viewing the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A, 1B, and 1C illustrate possible CSI-RS patterns in the LTEdownlink signal.

FIG. 2 illustrates a possible placement of CSI-RS symbols in an NRdownlink slot.

FIG. 3 illustrates an example distribution of selected beams in a cellsupporting 48 azimuthal beams.

FIG. 4 illustrates an example with 8 CSI-RS elements of 2 ports each,mapped to 2 REs in the physical layer OFDM grid, according to someembodiments.

FIG. 5 illustrates an example of sharing of two port CSI-RS elements,according to some embodiments.

FIG. 6 illustrates a grouping of CSI-RS elements into groups of 8,according to some embodiments.

FIG. 7 is a block diagram illustrating one of one or more nodes of awireless communication network, according to some embodiments.

FIG. 8 is a process flow diagram showing an example method performed bythe one or more nodes, according to some embodiments.

FIG. 9 is a block diagram illustrating a wireless device, according tosome embodiments.

FIG. 10 is a process flow diagram showing an example method performed bythe wireless device, according to some embodiments.

FIG. 11 is a block diagram of a functional implementation of one or morenodes of a wireless communication network, according to someembodiments.

FIG. 12 is a block diagram of a functional implementation of a wirelessdevice, according to some embodiments.

DETAILED DESCRIPTION

In the following, concepts in accordance with exemplary embodiments ofthe invention will be explained in more detail and with reference to theaccompanying drawings. The illustrated embodiments relate tochannel-state estimation in a wireless communication network, asperformed by wireless devices, in the following also referred to as UEs,and access nodes or base stations, also referred to herein as “gNBs.”The wireless communication network may for example be based on a 5Gradio access technology (RAT), such as the forthcoming 3GPP New Radio(NR) technology. However, it is to be understood that the illustratedconcepts could also be applied to other RATs.

It will be appreciated that the fifth generation of mobiletelecommunications and wireless technology is not yet fully defined, butis in an advanced draft stage within 3GPP, which includes work on 5G NRAccess Technology. LTE terminology is used in this disclosure in aforward-looking sense, to include equivalent 5G entities orfunctionalities although a different term is specified in 5G. Forinstance, eNBs in LTE are expected to be succeeded by gNBs, which areexpected to share some of the eNB's characteristics and capabilities.However, it will be appreciated that the application of the techniquesdescribed herein is not limited by the names placed on these nodes or bythe names applied to certain signals. A general description of theagreements on 5G NR Access Technology so far is contained in 3GPP TR38.802 V0.3.0 (2016-10), of which a draft version has been published asR1-1610848. Final specifications may be published in the future 3GPP TS38.2** series.

As suggested above, NR (or other wireless system) can utilize a pool ofN CSI-RS elements, where each element corresponds to a fixed number ofports, such as 2 ports. This pool of measurement resources may bedynamically shared among users in the cell depending on how the usersmove around in the cell (across beams) or whether particular users usebeamformed CSI-RS or non-precoded CSI-RS. Thus, at any given time, agiven UE may be configured to measure a single CSI-RS element, from theN CSI-RS elements that are potentially available in the downlink signalfor measurement, or may be configured to measure several or even all ofthe N CSI-RS elements. Multiple UEs may be configured to measure CSI-RSelements at the same time, using the same, distinct, or overlapping setsof CSI-RS elements. The gNB may signal to the UE which CSI-RS elementsthe UE shall measure on in a downlink control message referred to asdownlink control information (DCI).

It has been observed by the inventors, from measurements on manydifferent UE locations in a cell, that beam utilization is not likely tobe uniform over the set of possible beams. FIG. 3 illustrates an exampledistribution of selected beams in a cell supporting 48 azimuthal beams.The probability density function (PDF) is shown for each of the beamsthat are identified by the beam index. It can be seen from the figurethat there are five primary directions that can be identified in thiscell. As seen in the example distribution shown in FIG. 3, some beamsare very often selected and some very seldom. This has to do with thereflection environment in the covered cell. For example, there may be abuilding in a certain direction from the gNB, where the buildingreflects any beam transmitted in that direction towards the UEs in thecell.

Based on this observation, the techniques described herein introduce arestriction in the set of beams that can be simultaneously measured by aUE in the cell is introduced and this is reflected as a tree structurefor the signaling. More particularly, the tree structure introduces arestriction as to exactly which combinations of CSI-RS elements can besignaled, with this sacrifice in flexibility being offset by a reducednumber of bits being required for the signaling. An example treestructure is shown in FIG. 4, for an example configuration where eightCSI-RS elements of two ports each, i.e., where each CSI-RS element ismapped to two resource elements in the OFDM time-frequency grid.

In the example shown in FIG. 4, the UE can be instructed, with only afour-bit indication sent in the DCI, to measure one or several of apredetermined set of eight CSI-RS elements. Assuming that a differentbeam is mapped by the gNB to each of the eight different CSI-RS elements(with vertical and horizontal polarizations mapped to the two resourceelements per CSI-RS element), this four-bit indication can signal,according to the scheme illustrated in FIG. 4: eight differentsingle-beam assignments; four different two-beam assignments(represented by 0100, 0101, 1100, or 1101); two different four-beamassignments (represented by 0110 or 1110); and one eight-beam assignment(represented by 0111).

It will be appreciated that other groupings of CSI-RS elements arepossible. Further, it will be understood that the assignment of specificfour-bit indicators to groups in this example is arbitrary. However, theillustrated example is a particularly orderly approach, providing auniform hierarchy such that a UE can be instructed to measure eitherone, two, four, or eight CSI-RS elements with a simple four-bitindicator.

The realization that not all beams are equally likely to be used can beutilized in that the gNB can use the eight strongest beams for thesingle beam indicators (0000, 0001, 0010, 0011, 1000, 1001, 1010, 1011,in the example). These beams point in the “primary” directions and theset of “primary” directions is likely shared by the UEs in the cell butwith different orders of received signal strength. Any given UE can thenbe triggered to measure on a variable 1, 2, 4, 8, . . . beam directionsby using this 4-bit DCI. A single beam direction is used to update CSIfor a stationary UE, for example, since it is not likely to change itsbeam direction so frequently. Likewise, a measurement of a large numberof beams (such as eight, in this example) can be used to get an updateof the relative strengths of the primary beam directions.

Note that if all beams would be equally likely across the served UEs,then a length-N bitmap or a “N choose K” signaling scheme would beneeded to indicate the set of beams to measure on, which would requiremany more DCI bits than this tree based structure.

FIG. 5 illustrates an example of beam sharing among several UEs, UEs Ato E, again based on the example where eight two-port CSI-RS elementsare available. As seen in the figure, UE D has been instructed tomeasure all eight beams, while UE C is instructed to measure only asubset of four beams. UEs A and B in turn measure on two differentsubsets of those beams that UE C measures, while UE E measures a singlebeam. UE F shares only a single beam, with UE D, in the measurements.Hence, even though the system has a large number of beams (for example48), only eight beams are actually used in this measurement instant.Some UEs measure a single or a few of these eight while one UE ismeasuring all eight.

The illustrative examples of FIGS. 4 and 5 are based on the use of eighttwo-port CSI-RS elements. The presently disclosed techniques can beextended to any number of elements, and are not limited to the use oftwo-port CSI-RS elements. More generally, given N available CSI-RSelements, where each comprises one or multiple resource elements mappedto respective ports, a gNB can transmit reference signals on some or allof the N CSI-RS elements and a UE can measure on one, some, or all ofthe N elements. According to various embodiments, the gNB sends a K-bitidentifier, where K<N and where a first subset of the 2^(K) possiblevalues of the identifier each indicate that only a single respective oneof the N CSI-RS eleement should be measured, and each value of a second(distinct) subset of the 2^(K) possible values of the identifierindicates a specific combination of two or more CSI-RS elements thatshould be measured.

In a typical (but not necessarily every) embodiment, the first subsetwill comprise N different values, so that each one of the N CSI-RSelements can be individually identified. This is the case with theexample shown in FIG. 4, for instance.

An N-bit indicator would allow every possible combination of N CSI-RSelements to be signaled. As discussed above, however, this is notnecessary, and thus an N-bit indicator would be a wasteful use ofsignaling resources. With the restriction that K<N, it is apparent thatat most one-half of the possible subsets can be signaled, i.e., for thecase where K=N−1. However, even this is more than is likely to benecessary, in many systems. Thus, some embodiments of the presentlydisclosed techniques utilize a K-bit indicator where K=floor(log₂ N)+1or K=ceil(log₂ N)+1. (The “floor” function rounds a non-integer valuedown to the next smallest integer, while the “ceil” function rounds anon-integer value up to the next largest integer.) Typically, but notnecessarily, N of these indicator values would be used to indicateindividual CSI-RS elements, with the remaining values used to indicateone or more groups of CSI-RS elements. Using K=floor(log₂ N)+1 bitsensures that N values are available for this purpose, with at least oneleft over for signaling a group of CSI-RS elements. Using K=ceil(log₂N)+1 ensures that there are at least 2N values available, so that it ispossible to identify N or more groups of CSI-RS elements, in addition tobeing able to indicate each CSI-RS element individually. In someembodiments, however, K may be some other value that is greater thanceil(log₂ N), while still being less than N, allowing room forindicating many groups, but fewer than all of the full enumeration of2{circumflex over ( )}N arrangements.

In some embodiments, including the example shown in FIG. 4, N is a powerof 2, and log₂ N+1 bits are used for the identifier, with N of thevalues for the identifier corresponding to single CSI-RS elements. Theremaining N values can each be mapped to a combination of CSI-RSelements. In the illustrated example, this is an orderly mapping andhierarchical grouping, where N indicator values uniquely indicate singleCSI-RS elements, N/2 indicator values uniquely identify groups of twoCSI-RS elements, N/4 indicator values uniquely identify groups of fourCSI-RS elements, etc., but the grouping and mapping can be arbitrary, insome embodiments, so long as both the gNBs and the UEs agree on themapping of indicator values to CSI-RS elements and CSI-RS elementgroups.

In discussions of NR, the use of a 32-port CSI-RS resource is a workingassumption. The below discussion describes how the present techniquesmay be applied to this use case.

Two-port CSI-RS elements, as discussed above, may be further groupedinto groups of eight elements mapped across two OFDM symbols, preferablyconsecutive OFDM symbols. Each such group then contains 16 ports andthree such groups can be mapped to two resource blocks (i.e., 2×12=24subcarriers). This is shown in FIG. 6.

Given this mapping, the same tree structure as shown above in FIG. 4 canbe used within each one of these groups of eight two-port CSI-RSelements, such that a 4-bit indicator can be used to identify a CSI-RSelement within a group. Additional DCI signaling is used to indicate thegroup. Note that two bits are required to distinguish among threegroups.

A 32-port aggregated resource can be obtained by indicating two suchgroups. The two RBs shown in FIG. 6 can then be repeated across thedesired measurement bandwidth, hence each port is measured once per twoRBs in this example.

Since the signaling is dynamic in the DCI, it is possible to signal asingle CSI-RS element (two ports) as well as a four-port, eight-port,16-port, or 32-port CSI-RS resource by using this type of compressed andtree-based/hierarchical signaling structure. Note that six bits areneeded in this example.

Several approaches are possible for feedback signaling, i.e., where theUE reports its measurements and identifies one or more of the measuredCSI-RS elements. In some embodiments, the signaling payload is keptindependent on the number S of CSI-RS elements indicated to the UE tomeasure on, which according to some embodiments can vary according to 1,2, 4, 8, . . . .

In one example, the UE selects one out of S, where S is the number ofCSI-RS eleemnts that are measured, as implicitly indicated by the DCIused to trigger the CSI measurement and/or CSI report. An indicator ofof length M=ceil(log₂ S) (or ┌log₂ S┐) is signaled from the UE to thegNB, to point out which one of the N CSI-RS elements (or beams) thereport is referring to, together with the measurement result.Alternatively, the indicator length M is chosen to be equal to ceil(log₂S_(MAX)), where S_(MAX) is the maximum number of CSI-RS elements thatcan be measured (eight, in the example shown in FIG. 4). With thisapproach, the payload size is independent of S.

In another example, the UE selects Q out of S CSI-RS measurements toreport, where N is implicitly indicated by the DCI used to trigger theCSI measurement and/or CSI report. An indicator is signaled from the UEto gNB, to point out which Q out of the S CSI-RS elements (or beams) thereport is referring to, together with the Q measurement results.Alternatively, a bitmap length is chosen for this indicator so that thelargest combination of Q and S can always be covered, to make thesignaling payload size independent of Q and N. The benefit of thisembodiment is that the feedback control channel design and reception atthe gNB is less complex if the payload is kept constant or similar.Moreover, the transmit power of the UE (which depends on the payload) ismore stable.

It will be appreciated that the minimum time between the trigger of themeasurement from gNB to UE and the sending of the CSI report from the UEto the gNB may depend on the DCI field that indicates the CSI resources.In some embodiments, if the indication indicates many ports (such as0111 in the example above), then a predetermined parameter n₀₁₁₁ maydenote the number of subframes after which the report can betransmitted. Alternatively, if dynamic CSI report triggering is used,the gNB may request the UE to report not earlier than n₀₁₁₁ subframeslater. This can be captured in specifications as a table, which mapseach DCI triggering field value X (e.g., in the binary range from 0000to 1111) to a minimum subframe delay n_(X). A possible benefit from thisapproach is that the UE is allowed more time if the UE has to performmany measurements. If there is a single CSI-RS measurement, theprocessing time can be very short, and the UE may implicitly be assignedto transmit the report in the same subframe as the CSI-RS istransmitted, in some embodiments.

It will be appreciated that the techniques and apparatuses describedherein are especially applicable to recent technology trends that are ofparticular interest in a 5G NR context. These techniques are, however,also applicable in further development of the existing mobile broadbandsystems such as WCDMA and LTE.

FIG. 7 illustrates a diagram of a node, such as network node 30, whichmay be one of one or more nodes of a wireless communication network thatwork individually or collectively to perform the network sideembodiments described herein. The network node 30 may be, for example, anetwork access node such as a base station or gNodeB (in the 5G NRcontext). The network node 30 provides an air interface to a wirelessdevice, e.g., a 5G air interface for downlink transmission and uplinkreception, which is implemented via antennas 34 and a transceivercircuit 36. The transceiver circuit 36 may include transmitter circuits,receiver circuits, and associated control circuits that are collectivelyconfigured to transmit and receive signals according to a radio accesstechnology, for the purposes of providing cellular communication, orWLAN services if necessary. According to various embodiments, cellularcommunication services may be operated according to 5G. However, thisdoes not preclude the network node 30 from also being configured tohandle communications in any one or more of other 3GPP cellularstandards, GSM, GPRS, WCDMA, HSDPA, LTE and LTE-Advanced, ifappropriate. The network node 30 may also include communicationinterface circuits 38 for communicating with nodes in the core network,other peer radio nodes, and/or other types of nodes in the network.

The network node 30 also includes one or more processing circuits 32that are operatively associated with and configured to control thecommunication interface circuit(s) 38 and/or the transceiver circuit 36.The processing circuit 32 comprises one or more digital processors 42,e.g., one or more microprocessors, microcontrollers, Digital SignalProcessors (DSPs), Field Programmable Gate Arrays (FPGAs), ComplexProgrammable Logic Devices (CPLDs), Application Specific IntegratedCircuits (ASICs), or any combination thereof. More generally, theprocessing circuit 32 may comprise fixed circuitry, or programmablecircuitry that is specially configured via the execution of programinstructions implementing the functionality taught herein, or maycomprise some combination of fixed and programmable circuitry. Theprocessor(s) 42 may be multi-core. The processing circuit or circuits 32of one or more network nodes 30 (and possibly other controlling nodes)considered together may also be referred to as processing circuitry.Likewise, the transceiver circuits of the one or more network nodestogether can be referred to as transceiver circuitry. However, forconvenience, reference will be made to the processing circuit 32 and thetransceiver circuit 36 of a single network node 30.

The processing circuit 32 also includes a memory 44. The memory 44, insome embodiments, stores one or more computer programs 46 and,optionally, configuration data 48. The memory 44 provides non-transitorystorage for the computer program 46 and it may comprise one or moretypes of computer-readable media, such as disk storage, solid-statememory storage, or any combination thereof. By way of non-limitingexample, the memory 44 may comprise any one or more of SRAM, DRAM,EEPROM, and FLASH memory, which may be in the processing circuit 32and/or separate from the processing circuit 32. In general, the memory44 comprises one or more types of computer-readable storage mediaproviding non-transitory storage of the computer program 46 and anyconfiguration data 48 used by the node 30. Here, “non-transitory” meanspermanent, semi-permanent, or at least temporarily persistent storageand encompasses both long-term storage in non-volatile memory andstorage in working memory, e.g., for program execution.

In some embodiments, the network node 30 is configured to operate as oneof one or more network nodes of a wireless communication network forcontrolling the measurement of CSI-RS elements in a wirelesscommunication network. Accordingly, in some embodiments, the processingcircuit 32 is configured to transmit CSI-RS symbols in each of one ormore of N CSI-RS elements, each CSI-RS element in the set correspondingto at least one resource element in a time-frequency grid of resourceelements. The processing circuit 32 is configured to select, from the NCSI-RS elements, a first set of CSI-RS elements to be measured by afirst wireless device, the first set comprising one or several of the NCSI-RS elements and transmit, to the first wireless device, a messagecomprising a first K-bit indicator identifying the first set of CSI-RSelements, wherein K<N. The processing circuit 32 is also configured toreceive, from the first wireless device, in response to the message, ameasurement report corresponding to at least one of the first set ofCSI-RS elements. The first K-bit indicator is one of a predetermined setof K-bit indicators, where each member of the predetermined set of K-bitindicators uniquely corresponds to a CSI-RS element or group of CSI-RSelements from among the N CSI-RS, according to a predetermined mapping,such that each member of a first subset of the predetermined set ofK-bit indicators uniquely indicates a single one of the N CSI-RSelements and such that each member of a second subset of thepredetermined indicators uniquely indicates a predetermined group of twoor more of the N CSI-RS elements. This predetermined mapping may bedefined by industry standard, for example, such that the network node(e.g., gNB) and wireless device are programmed or hardcoded with thepredetermined mapping prior to being used. However, the predeterminedmapping may also be more dynamic in nature, e.g., such that networksignaling indicates which of a set of predetermined mappings isapplicable at any given time, or such that the wireless device isconfigured with all or part of the predetermined mapping viaover-the-air signaling.

Regardless of its specific implementation details, the processingcircuit 32 of the network node 30 is configured to perform (possibly incoordination with other nodes) a method according to one or more of thetechniques described above, such as method 800 of FIG. 8. The method 800includes transmitting CSI-RS symbols in each of one or more of N CSI-RSelements, each CSI-RS element in the set corresponding to at least oneresource element in a time-frequency grid of resource elements (block802). The method 800 includes selecting, from the N CSI-RS elements, afirst set of CSI-RS elements to be measured by a first wireless device,the first set comprising one or several of the N CSI-RS elements (block804). The method 800 also includes transmitting, to the first wirelessdevice, a message comprising a first K-bit indicator identifying thefirst set of CSI-RS elements, wherein K<N (block 806). The method 800further includes receiving, from the first wireless device, in responseto the message, a measurement report corresponding to at least one ofthe first set of CSI-RS elements (block 808). The first K-bit indicatoris one of a predetermined set of K-bit indicators, where each member ofthe predetermined set of K-bit indicators uniquely corresponds to aCSI-RS element or group of CSI-RS elements from among the N CSI-RS,according to a predetermined mapping, such that each member of a firstsubset of the predetermined set of K-bit indicators uniquely indicates asingle one of the N CSI-RS elements and such that each member of asecond subset of the predetermined indicators uniquely indicates apredetermined group of two or more of the N CSI-RS elements. In somecases, K=ceil(log₂ N)+1.

Each of the N CSI-RS elements may comprise a pair of resource elementsin an OHM resource element grid, and transmitting CSI-RS symbols in eachof the one or more of the N CSI-RS elements may include transmitting inone of the pair of resource elements with a first antenna polarizationand transmitting in the other of the pair of resource elements with asecond antenna polarization, the second antenna polarization beingsubstantially orthogonal to the first.

In some cases, the base station may map specific beams to CSI-RSelements. Accordingly, transmitting CSI-RS symbols in each of the one ormore of the N CSI-RS elements includes transmitting a beamformed CSI-RSsymbol in at least one of the CSI-RS elements. Transmitting CSI-RSsymbols in each of the one or more of the N CSI-RS elements may includetransmitting beamformed CSI-RS symbols in each of N CSI-RS elements,such that each CSI-RS element corresponds to a different transmit beam.The method 800 may further include selecting N transmit beams from a setof B available beams, where B>N, and wherein each CSI-RS elementcorresponds to a different one of the selected transmit beams. Theselection of the N transmit beams may be based on previously receivedmeasurement reports, and the selected beams may include at least onebeam from each of a plurality of angularly spaced apart primary beamdirections, the primary directions being determined from the previouslyreceived measurement reports.

As to the hierarchical tree pattern of the signaling, the first subsetof the predetermined set of K-bit indicators may consist of Nindicators, each uniquely indicating a single one of the N CSI-RSelements. In some cases, N is a power of 2, and K=log₂ N+1. The firstsubset of the predetermined set of K-bit indicators may consist of Nindicators, each uniquely indicating a single one of the N CSI-RSelements, and the second subset may include N/2 indicators that eachuniquely identify a group of two CSI-RS elements from the N CSI-RSelements. In some cases, such as when K≥8, the second subset may furtherinclude N/4 indicators that each uniquely identify a group of fourCSI-RS elements from the N CSI-RS elements. This pattern may continue,of course, consistent with the binary tree approach described herein.

The second subset may include one indicator that indicates that all NCSI-RS elements are to be measured. The message comprising the K-bitindicator may be a DCI message.

The method 800 may include selecting, from the N CSI-RS elements, asecond set of CSI-RS elements to be measured by a second wireless devicein an interval of time that at least partly overlaps an interval of timein which the first wireless device is measuring the first set of CSI-RSelements, the second set comprising one or several of the N CSI-RSelements and differing from the first set. The method 800 may furtherinclude transmitting, to the second wireless device, a messagecomprising a second K-bit indicator identifying the second set of CSI-RSelements, wherein the second K-bit indicator is one of the predeterminedset of K-bit indicators. The method 800, in this case, may includereceiving, from the second wireless device, in response to the message,a measurement report corresponding to at least one of the second set ofCSI-RS elements. The first K-bit indicator may indicate a first group oftwo or more of the N CSI-RS elements and the second K-bit indicator mayindicate a second group of two or more the N CSI-RS elements, the firstand second groups being mutually exclusive.

With regard to any feedback signaling, the measurement report receivedfrom the first wireless device comprises, in some cases, an M-bitindicator indicating one of the CSI-RS elements in the first set ofCSI-RS elements, where M equals ceil(log₂ S) and S equals the number ofmembers in the first set of CSI-RS elements. In other cases, themeasurement report received from the first wireless device comprises anM-bit indicator indicating one of the CSI-RS elements in the first setof CSI-RS elements, where M equals ceil(log₂ S_(MAX)) and S_(MAX) equalsthe maximum number of members in any one of the predetermined groups oftwo or more of the N CSI-RS elements that can be indicated with thepredetermined set of K-bit indicators.

In some cases, the measurement report received from the first wirelessdevice comprises an M-bit indicator indicating one of the CSI-RSelements in the first set of CSI-RS elements, where M equals ceil(log₂S) and S equals the number of members in the first set of CSI-RSelements. In some cases, the measurement report comprises measurementdata for Q of the CSI-RS elements, where 1<Q<S, S being the number ofmembers in the first set of CSI-RS elements, and wherein the measurementreport further includes an indicator identifying which Q of the Smembers in the first of CSI-RS elements are represented in themeasurement report.

FIG. 9 illustrates an example wireless device 50 (e.g., UE) that isconfigured to perform the techniques described herein for the wirelessdevice. The wireless device 50 may also be considered to represent anywireless devices that may operate in a network, such as a 5G network.The wireless device 50 herein can be any type of wireless device capableof communicating with a network node or another UE over radio signals.The wireless device 50 may also be referred to, in various contexts, asa radio communication device, a target device, a device-to-device (D2D)UE, a machine-type UE or UE capable of machine to machine (M2M)communication, a sensor-equipped UE, a PDA (personal digital assistant),a wireless tablet, a mobile terminal, a smart phone, laptop-embeddedequipment (LEE), laptop-mounted equipment (LME), a wireless USB dongle,a Customer Premises Equipment (CPE), etc.

The wireless device 50 communicates with one or more radio nodes or basestations, such as one or more network nodes 30, via antennas 54 and atransceiver circuit 56. The transceiver circuit 56 may includetransmitter circuits, receiver circuits, and associated control circuitsthat are collectively configured to transmit and receive signalsaccording to a radio access technology, for the purposes of providingcellular communication services.

The wireless device 50 also includes one or more processing circuits 52that are operatively associated with and control the radio transceivercircuit 56. The processing circuit 52 comprises one or more digitalprocessing circuits, e.g., one or more microprocessors,microcontrollers, DSPs, FPGAs, CPLDs, ASICs, or any mix thereof. Moregenerally, the processing circuit 52 may comprise fixed circuitry, orprogrammable circuitry that is specially adapted via the execution ofprogram instructions implementing the functionality taught herein, ormay comprise some mix of fixed and programmed circuitry. The processingcircuit 52 may be multi-core.

The processing circuit 52 also includes a memory 64. The memory 64, insome embodiments, stores one or more computer programs 66 and,optionally, configuration data 68. The memory 64 provides non-transitorystorage for the computer program 66 and it may comprise one or moretypes of computer-readable media, such as disk storage, solid-statememory storage, or any mix thereof. By way of non-limiting example, thememory 64 comprises any one or more of SRAM, DRAM, EEPROM, and FLASHmemory, which may be in the processing circuit 52 and/or separate fromprocessing circuit 52. In general, the memory 64 comprises one or moretypes of computer-readable storage media providing non-transitorystorage of the computer program 66 and any configuration data 68 used bythe user equipment 50.

Accordingly, in some embodiments, the processing circuit 52 of thewireless device 50 is configured to measure CSI-RS of a wirelesscommunication network. The processing circuit 52 is configured toreceive, from the wireless communication network, a message comprising afirst K-bit indicator and use the first K-bit indicator to identify afirst set of CSI-RS from N CSI-RS elements, wherein each CSI-RS elementcorresponds to at least one resource element in a time-frequency grid ofresource elements and wherein K<N. The processing circuit 52 isconfigured to perform measurements on the identified first set of CSI-RSelements and send, to the wireless communications network, a measurementreport corresponding to at least one of the first set of CSI-RSelements. The first K-bit indicator is one of a predetermined set ofK-bit indicators, where each member of the predetermined set of K-bitindicators uniquely corresponds to a CSI-RS element or group of CSI-RSelements from among the N CSI-RS, according to a predetermined mapping,such that each member of a first subset of the predetermined set ofK-bit indicators uniquely indicates a single one of the N CSI-RSelements and such that each member of a second subset of thepredetermined indicators uniquely indicates a predetermined group of twoor more of the N CSI-RS elements.

Regardless of its specific implementation details, the processingcircuit 52 of the wireless device 50 is configured to perform a methodaccording to one or more of the techniques described, such as method1000 of FIG. 10. The method 1000 includes receiving, from the wirelesscommunication network, a message comprising a first K-bit indicator(block 1002) and using the first K-bit indicator to identify a first setof CSI-RS from N CSI-RS elements, wherein each CSI-RS elementcorresponds to at least one resource element in a time-frequency grid ofresource elements and wherein K<N (block 1004). The method 1000 alsoincludes performing measurements on the identified first set of CSI-RSelements (block 1006) and sending, to the wireless communicationsnetwork, a measurement report corresponding to at least one of the firstset of CSI-RS elements (block 1008). The first K-bit indicator is one ofa predetermined set of K-bit indicators, where each member of thepredetermined set of K-bit indicators uniquely corresponds to a CSI-RSelement or group of CSI-RS elements from among the N CSI-RS, accordingto a predetermined mapping, such that each member of a first subset ofthe predetermined set of K-bit indicators uniquely indicates a singleone of the N CSI-RS elements and such that each member of a secondsubset of the predetermined indicators uniquely indicates apredetermined group of two or more of the N CSI-RS elements. In somecases, K=ceil(log₂ N)+1.

Each of the N CSI-RS elements may comprise a pair of resource elementsin an OFDM resource element grid, and where, for each CSI-RS element aCSI-RS symbol is transmitted in one of the pair of resource elementswith a first antenna polarization and a CSI-RS is transmitted in theother of the pair of resource elements with a second antennapolarization, the second antenna polarization being substantiallyorthogonal to the first, and the method 1000 may include performingmeasurements on the identified first set of CSI-RS elements comprises,for each CSI-RS element, combining measurements of the pair of resourceelements.

The first subset of the predetermined set of K-bit indicators mayconsist of N indicators, each uniquely indicating a single one of the NCSI-RS elements.

In some cases, N is a power of 2, and K=log₂ N+1. The first subset ofthe predetermined set of K-bit indicators may consist of N indicators,each uniquely indicating a single one of the N CSI-RS elements, andwherein the second subset includes N/2 indicators that each uniquelyidentify a group of two CSI-RS elements from the N CSI-RS elements. Incases where K≥8, the second subset further includes N/4 indicators thateach uniquely identify a group of four CSI-RS elements from the N CSI-RSelements.

The second subset may include one indicator that indicates that all NCSI-RS elements are to be measured. The message may comprise the K-bitindicator is a DCI message.

The method 1000 may include, in the measurement report sent to thewireless communications network, an M-bit indicator indicating one ofthe CSI-RS elements in the first set of CSI-RS elements, where M equalsceil(log₂ S) and S equals the number of members in the first set ofCSI-RS elements. The method 1000 may include, in the measurement reportsent to the wireless communications network, an M-bit indicatorindicating one of the CSI-RS elements in the first set of CSI-RSelements, where M equals ceil(log₂ S_(MAX)) and S_(MAX) equals themaximum number of members in any one of the predetermined groups of twoor more of the N CSI-RS elements that can be indicated with thepredetermined set of K-bit indicators.

The method 1000 may include, in the measurement report sent to thewireless communications network, an M-bit indicator indicating one ofthe CSI-RS elements in the first set of CSI-RS elements, where M equalsceil(log₂ S) and S equals the number of members in the first set ofCSI-RS elements. The method 1000 may include, in the measurement reportsent to the wireless communications network, measurement data for Q ofthe CSI-RS elements, where 1<Q<S, S being the number of members in thefirst set of CSI-RS elements, and further including in the measurementreport an indicator identifying which Q of the S members in the first ofCSI-RS elements are represented in the measurement report. As discussedin detail above, the techniques described herein, e.g., as illustratedin the process flow diagrams of FIGS. 8 and 10, may be implemented, inwhole or in part, using computer program instructions executed by one ormore processors. It will be appreciated that a functional implementationof these techniques may be represented in terms of functional modules,where each functional module corresponds to a functional unit ofsoftware executing in an appropriate processor or to a functionaldigital hardware circuit, or some combination of both.

FIG. 11 illustrates an example functional module or circuit architectureas may be implemented in a network node 30 operating as one or morenodes of a wireless communication network configured to control themeasurement of CSI-RS elements in the wireless communication network.The implementation includes a transmitting module 1102 for transmittingCSI-RS symbols in each of one or more of N CSI-RS elements, each CSI-RSelement in the set corresponding to at least one resource element in atime-frequency grid of resource elements. The implementation alsoincludes a selecting module 1104 for selecting, from the N CSI-RSelements, a first set of CSI-RS elements to be measured by a firstwireless device, the first set comprising one or several of the N CSI-RSelements. The transmitting module 1102 is also for transmitting, to thefirst wireless device, a message comprising a first K-bit indicatoridentifying the first set of CSI-RS elements, wherein K<N. Theimplementation also includes a receiving module 1106 for receiving, fromthe first wireless device, in response to the message, a measurementreport corresponding to at least one of the first set of CSI-RSelements. The first K-bit indicator is one of a predetermined set ofK-bit indicators, where each member of the predetermined set of K-bitindicators uniquely corresponds to a CSI-RS element or group of CSI-RSelements from among the N CSI-RS, according to a predetermined mapping,such that each member of a first subset of the predetermined set ofK-bit indicators uniquely indicates a single one of the N CSI-RSelements and such that each member of a second subset of thepredetermined indicators uniquely indicates a predetermined group of twoor more of the N CSI-RS elements.

FIG. 12 illustrates an example functional module or circuit architectureas may be implemented in a wireless device 50 configured to measureCSI-RS elements in a wireless communication network. The implementationincludes a receiving module 1202 for receiving, from the wirelesscommunication network, a message comprising a first K-bit indicator andan identifying module 1204 for using the first K-bit indicator toidentify a first set of CSI-RS from N CSI-RS elements, wherein eachCSI-RS element corresponds to at least one resource element in atime-frequency grid of resource elements and wherein K<N. Theimplementation also includes a measuring module 1206 for performingmeasurements on the identified first set of CSI-RS elements and asending module 1208 for sending, to the wireless communications network,a measurement report corresponding to at least one of the first set ofCSI-RS elements. The first K-bit indicator is one of a predetermined setof K-bit indicators, where each member of the predetermined set of K-bitindicators uniquely corresponds to a CSI-RS element or group of CSI-RSelements from among the N CSI-RS, according to a predetermined mapping,such that each member of a first subset of the predetermined set ofK-bit indicators uniquely indicates a single one of the N CSI-RSelements and such that each member of a second subset of thepredetermined indicators uniquely indicates a predetermined group of twoor more of the N CSI-RS elements.

Notably, modifications and other embodiments of the disclosedinvention(s) will come to mind to one skilled in the art having thebenefit of the teachings presented in the foregoing descriptions and theassociated drawings. Therefore, it is to be understood that theinvention(s) is/are not to be limited to the specific embodimentsdisclosed and that modifications and other embodiments are intended tobe included within the scope of this disclosure. Although specific termsmay be employed herein, they are used in a generic and descriptive senseonly and not for purposes of limitation.

What is claimed is:
 1. A method for controlling the measurement ofchannel-state information reference signal (CSI-RS) elements in awireless communication network, the method comprising, in one or morenodes of the wireless communication network: transmitting, to a firstwireless device, a message comprising a first K-bit indicatoridentifying a first set of CSI-RS elements selected from N transmittedCSI-RS elements, wherein K<N; and receiving, from the first wirelessdevice, in response to the message, a measurement report correspondingto at least one of the first set of CSI-RS elements, wherein the firstK-bit indicator is one of a predetermined set of K-bit indicators, whereeach member of the predetermined set of K-bit indicators uniquelycorresponds to a CSI-RS element or group of CSI-RS elements from amongthe N CSI-RS, according to a predetermined mapping, such that eachmember of a first subset of the predetermined set of K-bit indicatorsuniquely indicates a single one of the N CSI-RS elements, the firstsubset comprising N indicators, and such that each member of a secondsubset of the predetermined indicators uniquely indicates apredetermined group of two or more of the N CSI-RS elements.
 2. Themethod of claim 1, wherein K>ceil(log₂ N) or K=ceil(log₂ N)+1.
 3. Themethod of claim 1, wherein each of the N CSI-RS elements comprises apair of resource elements in an Orthogonal Frequency-DivisionMultiplexing (OFDM) resource element grid.
 4. The method of claim 1,wherein N is a power of 2, and K=log₂ N+1, wherein the first subset ofthe predetermined set of K-bit indicators consists of N indicators, eachuniquely indicating a single one of the N CSI-RS elements, and whereinthe second subset includes N/2 indicators that each uniquely identify agroup of two CSI-RS elements from the N CSI-RS elements.
 5. The methodof claim 1, further comprising: transmitting, to a second wirelessdevice, a message comprising a second K-bit indicator identifying asecond set of CSI-RS elements among the N CSI-RS elements to be measuredby the second wireless device in an interval of time that at leastpartly overlaps an interval of time in which the first wireless deviceis measuring the first set of CSI-RS elements, wherein the second K-bitindicator is one of the predetermined set of K-bit indicators; andreceiving, from the second wireless device, in response to the message,a measurement report corresponding to at least one of the second set ofCSI-RS elements.
 6. The method of claim 5, wherein the first K-bitindicator indicates a first group of two or more of the N CSI-RSelements and the second K-bit indicator indicates a second group of twoor more the N CSI-RS elements, the first and second groups beingmutually exclusive.
 7. The method of claim 1, wherein the measurementreport received from the first wireless device comprises an M-bitindicator indicating one of the CSI-RS elements in the first set ofCSI-RS elements, where M equals ceil(log₂ S) and S equals the number ofmembers in the first set of CSI-RS elements.
 8. The method of claim 1,wherein the measurement report received from the first wireless devicecomprises an M-bit indicator indicating one of the CSI-RS elements inthe first set of CSI-RS elements, where M equals ceil(log₂ S_(MAX)) andS_(MAX) equals the maximum number of members in any one of thepredetermined groups of two or more of the N CSI-RS elements that can beindicated with the predetermined set of K-bit indicators.
 9. The methodof claim 1, wherein the measurement report received from the firstwireless device comprises an M-bit indicator indicating one of theCSI-RS elements in the first set of CSI-RS elements, where M equalsceil(log₂ S) and S equals the number of members in the first set ofCSI-RS elements.
 10. The method of claim 1, wherein the measurementreport comprises measurement data for Q of the CSI-RS elements, where1<Q<S, S being the number of members in the first set of CSI-RSelements, and wherein the measurement report further includes anindicator identifying which Q of the S members in the first of CSI-RSelements are represented in the measurement report.
 11. A method formeasuring channel-state information reference signal (CSI-RS) elementsin a wireless communication network, the method comprising, in awireless device: using a first K-bit indicator received from thewireless communication network to identify a first set of CSI-RSelements from a set of N CSI-RS elements, wherein each CSI-RS elementcorresponds to at least one resource element in a time-frequency grid ofresource elements and wherein K<N; and performing measurements on theidentified first set of CSI-RS elements; wherein the first K-bitindicator is one of a predetermined set of K-bit indicators, where eachmember of the predetermined set of K-bit indicators uniquely correspondsto a CSI-RS element or group of CSI-RS elements from among the N CSI-RS,according to a predetermined mapping, such that each member of a firstsubset of the predetermined set of K-bit indicators uniquely indicates asingle one of the N CSI-RS elements and such that each member of asecond subset of the predetermined indicators uniquely indicates apredetermined group of two or more of the N CSI-RS elements, wherein thefirst subset of the predetermined set of K-bit indicators consists of Nindicators, each uniquely indicating a single one of the N CSI-RSelements.
 12. The method of claim 11, wherein K>ceil(log₂ N) orK=ceil(log₂ N)+1.
 13. The method of claim 11, wherein each of the NCSI-RS elements comprises a pair of resource elements in an OrthogonalFrequency-Division Multiplexing (OFDM) resource element grid, andwherein performing measurements on the identified first set of CSI-RSelements comprises, for each CSI-RS element, combining measurements ofthe pair of resource elements.
 14. The method of claim 11, wherein N isa power of 2, and K=log₂ N+1, and wherein the first subset of thepredetermined set of K-bit indicators consists of N indicators, eachuniquely indicating a single one of the N CSI-RS elements, and whereinthe second subset includes N/2 indicators that each uniquely identify agroup of two CSI-RS elements from the N CSI-RS elements.
 15. The methodof claim 14, wherein K≥8 and wherein the second subset further includesN/4 indicators that each uniquely identify a group of four CSI-RSelements from the N CSI-RS elements.
 16. The method of claim 11, whereinthe second subset includes one indicator that indicates that all NCSI-RS elements are to be measured.
 17. The method of claim 11, whereinthe method further comprises sending, in a measurement report sent tothe wireless communications network, an M-bit indicator indicating oneof the CSI-RS elements in the first set of CSI-RS elements, where Mequals ceil(log₂ S) and S equals the number of members in the first setof CSI-RS elements.
 18. The method of claim 11, wherein the methodfurther comprises sending, in a measurement report sent to the wirelesscommunications network, an M-bit indicator indicating one of the CSI-RSelements in the first set of CSI-RS elements, where M equals ceil(log₂S_(MAX)) and S_(MAX) equals the maximum number of members in any one ofthe predetermined groups of two or more of the N CSI-RS elements thatcan be indicated with the predetermined set of K-bit indicators.
 19. Themethod of claim 11, wherein the method further comprises sending, in ameasurement report sent to the wireless communications network,measurement data for Q of the CSI-RS elements, where 1<Q<S, S being thenumber of members in the first set of CSI-RS elements, and furtherincluding in the measurement report an indicator identifying which Q ofthe S members in the first of CSI-RS elements are represented in themeasurement report.
 20. A wireless device configured to measurechannel-state information reference signal (CSI-RS) elements in awireless communication network, comprising: transceiver circuitry; andprocessing circuitry operatively associated with the transceivercircuitry and configured to: use a first K-bit indicator received fromthe wireless communication network to identify a first set of CSI-RSelements from a set of N CSI-RS elements, wherein each CSI-RS elementcorresponds to at least one resource element in a time-frequency grid ofresource elements and wherein K<N; and send, to the wirelesscommunications network, a measurement report corresponding to at leastone of the first set of CSI-RS elements; wherein the first K-bitindicator is one of a predetermined set of K-bit indicators, where eachmember of the predetermined set of K-bit indicators uniquely correspondsto a CSI-RS element or group of CSI-RS elements from among the N CSI-RS,according to a predetermined mapping, such that each member of a firstsubset of the predetermined set of K-bit indicators uniquely indicates asingle one of the N CSI-RS elements and such that each member of asecond subset of the predetermined indicators uniquely indicates apredetermined group of two or more of the N CSI-RS elements, wherein thefirst subset of the predetermined set of K-bit indicators consists of Nindicators, each uniquely indicating a single one of the N CSI-RSelements.